The continuous measure of the tension in a filament while it is moving and particularly of a textile filament, is utilized to control a number of operations effected on the filament in the course of its manufacture, as well as at the time of its utilization.
This measure poses problems of wear resulting from the frictional contact of the filament on the surface of the support for measuring the pressure. There exist a number of solutions, certain ones utilizing a diversion system formed by three rollers of which the middle wheel is carried by an elastic arm whose deformation is measured. The most perfected arrangement is constituted by a sapphire surface connected to a piezo-electric pressure receiver. However, even a material as hard as sapphire cannot resist the resulting contact wear and it becomes deformed.
There also exists operations in the textile field, in the course of which it is desirable to measure the tension in the filament, but which are unfortunately incompatable with the contact of the filament against the surface of the support of the measuring device. This is notably the case for the measurement of the tension of a filament produced by a spinning device with a ring slider. In fact, on such devices the torsion is transferred to the filament by the rotation of the bobbin and of the slider on the ring and this torsion is transmitted to the drawing assembly which delivers the fibers which are then captured by the extremity of the filament during formation. Because of this fact, it is impossible to measure the tension of the filament between the ring slider and the drawing assembly without the contact of the filament on the surface of the measuring support preventing the torsion from communicating to the outlet of the drawing assembly.